Cathode and process of making the same



Patented Nov. 3, 1931 UNITED STATES PATENT OFFICE AUGUST GEHRTS, 0F FRIEDENAU, BERLIN, AND HANS KOLLIGS, O F BERLIN, GERMANY, ASSIGNORS TO SIEMENS & HALSKE AKTIENGESELLSCHAFT, OF SIEMENSSTAQDT, NEAR BERLIN, GERMANY, A GERMAN COMPANY CATHODE AND PROCESS OF MAKING THE SAME 1% Drawing. Application filed April 2, 1928, Serial No. 266,866, and in Germany April 2, 1927.

This invention relates to cathodes and the process of making them. More particularly, the invention relates to a method of applying the thermionically active coating to said cathodes.

Heretofore, it has been the practice to employ an oxygen compound of the alkaline earth metal group as the emissive body of an electron discharge device to obtain highly active cathodes,

According to this invention a substantially higher emissivity is obtained by using as V the emissive body, the alkalineearth metal itself, e. g., barium or a mixture or alloy of several alkaline earth metals.

A cathode of such alkaline earth metals can be prepared, for instance, by applying an alkaline earth metal to a carrier by vaporizing or sublimating the alkaline earth metal upon the carrier in a vacuum.

Before applying the metal, it is desirable to provide the carrier with an intermediate layer, e. g., barium oxide which may also be applied by vaporization. The substances may be vaporized from a specially provided electrode or from one of the existing electrodes in the device, for instance, the anode.

In order to accelerate the pumping process and to eliminate certain residual gases, it is advantageous to apply getter substances, these being preferably vaporized by raising the temperature as they are used for building up the cathode.

The evacuation must be continued before the application of the last metal layer to such an extent that no occluded gases are evolved from the electrodes.

A cathode produced in this manner is not to be considered as an. oxide cathode as it is proved by the fact that upon adding a small quantity of oxygen which oxidizes the metallic layer, the electron yield drops to a third or a quarter of its former value. Furthermore, the electron yield is considerably higher than with an oxide cathode, namely 200 to 4100 milliamperes per watt when the cathode is scarcely visibly glowing.

The new cathode is suitable for application both in high vacuum as well as in an atmosphere of noble gases, e. g., argon and may also be applied to advantage for indirect heating and in tubes in Which the smallest possible voltage drop is desired at the cathode.

What is claimed is:

The method of making a cathode for an electron discharge device which comprises oxidizing a cathode core with alkaline earth oxide, inserting the oxidized core in an evacuated vessel containing alkaline earth metal in a pure state, heating the alkaline earth metal to vaporizing temperature, and depositing the metal on the oxidized core.

In witness whereofwe hereunto subscribe our names, this 20th day of March, 1928.

AUGUST GEHRTS.

HANS KOLLIGS. 

